In engine valves for vehicle engines, vehicle valve stem seals are used to control the amount of engine oil supplied to a sliding surface between a valve stem (valve axis) and a valve stem guide (valve bearing), and to seal exhaust gases and the like.
Patent Document 1 discloses a structure of a sliding portion in which a film layer comprising a diamond-like hard carbon film is formed on the inner circumference of the seal member to be fitted around a valve stem for the purpose of reducing sliding resistance between a seal member and a valve stem.
Patent Document 2 discloses a valve stem seal containing a fluorine resin film on a sliding surface of the inner circumference of a seal lip portion.
Patent Document 3 discloses formation of some or the whole part of a valve stem oil seal member including sliding surfaces with a lubricating rubber composition which includes thermoplastic fluororesin, fluororubber, and a fluoropolymer of a low molecular weight, in order to improve durability and sealing performance.
In recent years, improvement in sliding properties of vehicle valve stem seals is desired along with the demand for higher performance (higher rotations) and better fuel economy of vehicle engines. For sure, a vehicle valve stem seal formed of fluororubber or silicone rubber is likely to have better sliding properties compared to a vehicle valve stem seal formed of acrylic rubber or nitrile rubber. The above-mentioned demand requires further improvement in sliding properties.
Patent Document 1: JP 2005-180329 A
Patent Document 2: JP 9-68011 A
Patent Document 3: JP 6-49438 A